Conjecture and hypothesis: The importance of reality checks

Conjecture and hypothesis: The importance of reality checks David Deamer Commentary Address: Department of Biomolecular Engineering, University of California, Santa Cruz CA 95060, USA Email: David Deamer - Keywords: hydrothermal fields; hydrothermal vents; origin of life; polymerization by condensation; protocells Open Access Beilstein J. Org. Chem. 2017, 13, 620–624. doi:10.3762/bjoc.13.60 Received: 01 January 2017 Accepted: 15 March 2017 Published: 28 March 2017 This article is part of the Thematic Series "From prebiotic chemistry to molecular evolution". Guest Editor: L. Cronin © 2017 Deamer; licensee Beilstein-Institut. License and terms: see end of document. Abstract In origins of life research, it is important to understand the difference between conjecture and hypothesis. This commentary explores the difference and recommends alternative hypotheses as a way to advance our understanding of how life can begin on the Earth and other habitable planets. As an example of how this approach can be used, two conditions have been proposed for sites conducive to the origin of life: hydrothermal vents in salty seawater, and fresh water hydrothermal fields associated with volcanic landmasses. These are considered as alternative hypotheses and the accumulating weight of evidence for each site is described and analyzed. Introduction The word conjecture is defined as an opinion based on incomplete information. The word can be taken to be slightly pejorative, but given that conjecture also involves imagination and creative effort, I will argue here that in scientific research there is a natural progression from conjecture to hypothesis to consensus. Conjecture is an idea, hypothesis is a conjecture that can be tested by experiment or observation, and consensus emerges when other interested colleagues agree that evidence supports a hypothesis that has explanatory value. This approach is clearly relevant to origins of life research which is still at a stage where multiple conjectures abound yet vast gaps in knowledge and understanding remain, mostly due to lack of signifi- cant funding for research in this area. The result is that only a few dozen laboratories are supported in the global scientific community, in contrast to thousands of scientists investigating health related research or chemistry and physics having applications in industry. Another reason is that the origin of life is best understood in interdisciplinary terms involving knowledge of astronomy, planetary science, biophysics, chemistry and biochemistry, molecular biology and evolution. Relatively few scientists have a taste for research that demands such broad knowledge to make significant advances. The historical development of origins research has been well described by Iris Fry [1] and Antonio Lazcano [2]. 620 Beilstein J. Org. Chem. 2017, 13, 620–624. Discussion Most scientists agree that hypothesis testing is an essential feature of research, and a typical proposal to a funding agency usually has a clearly stated hypothesis. However, there is a very human tendency for investigators to prefer positive results that support their idea. Karl Popper [3] had some good advice in this regard: Don't try to prove an idea is right. Instead, try to falsify it. Those rare ideas that cannot be falsified then emerge from the majority of ideas that fail the testing process. Günther Wächtershäuser [4] recently commented on how Popper's advice can be applied in origins of life research. Hypothesis testing is an essential feature of good research, but its value can be increased by one additional step which was first clearly stated in 1964 by John Platt [5]. The title of Platt's article was Strong Inference, which he defines in the following way: “Strong inference consists of applying the following steps to every problem in science, formally and explicitly and regularly. Conjecture: life originated in hydrothermal vents and later adapted to fresh water on volcanic and continental land masses. In the absence of alternatives this idea has been accepted as a reasonable suggestion. Is there an alternative? Here is another list of facts: • A small fraction of the Earth's water is distilled from seawater and precipitates as fresh water on volcanic land masses. • The water accumulates in hydrothermal fields that undergo cycles of evaporation and refilling. • During evaporation, dilute solutes in the water become concentrated films on mineral surfaces. • If the solutes can undergo chemical or physical interactions, they will do so in the concentrated films. • The products will accumulate in the pools when water returns either in the form of precipitation or as fluctuations in water levels related to hot springs or geyser activity. 1. Devising alternative hypotheses. 2. Devising crucial experiments ... with alternative possible outcomes, each of which will, as nearly as possible, exclude one or more of the hypotheses. 3. Carrying out the experiment so as to get a clean result.” Conjecture: life originated in fresh water hydrothermal fields associated with volcanic land masses, then adapted to the salty seawater of the early ocean. Research approaches that incorporate alternative hypotheses avoid the tendency to prefer positive results, because both positive and negative results have value in inferring which of the two alternatives is better supported by accumulating evidence. The aim of this commentary is to describe how alternative hypotheses can be applied to understanding the origin of life, with the focus on a simple question: Did life begin in salty water in a marine environment, or did life begin in fresh water in a terrestrial setting? Although the question seems simple, there are significant ramifications of possible answers for life detection missions to other planetary objects in the solar system. Now we can provide a few more details about two geophysical conditions that have been proposed as alternative sites conducive for the origin of life. Hydrothermal vents were discovered in 1977 [6] and were soon proposed to be a likely site for life to begin [7-10]. Hydrothermal vents referred to as black smokers are produced when seawater comes into contact with rocks heated by magma underlying mid-ocean ridges. The hot water dissolves mineral components of the rock and then emerges through the ocean floor where the mineral solutes come out of solution to form characteristic chimneys that emit a black smoke of precipitated metal sulfide particles. We can begin with two conjectures and then attempt to turn them into alternative hypotheses. The first conjecture follows from the discovery of hydrothermal vents and observations related to their properties: A second type of hydrothermal vent was discovered in 2001 [11] that does not depend on volcanism. Instead they form when seawater reacts with mineral components of peridotite in the sea floor, a process called serpentinization. The reaction produces hydrogen and a stro (...truncated)